This invention relates to a method of extracting methane dissolved in water which saturates certain coal beds. More particularly, it relates to a method which may not require the drilling of wells, the upgrading of existing roads, the construction of new roads on currently undisturbed lands, or the construction of a network of new pipelines across public and/or private lands. It may proceed without generating offensive noise or raising dust clouds. It may not cause disturbance to surface lands or require their restoration. It may not bring about a decrease in local property values. It may not lead to increased erosion or sedimentation in the areas where the resource is located or downstream from these areas. It may not result in the extraction of salt or salt water from the coal beds. It may not cause contamination of surface or ground water, and may therefore not affect either the quality or the quantity of currently used water resources. It may result in the extraction of a greater fraction of the methane from the same resources, and thus produce a much greater amount of energy from them, when compared to currently used methods. It may also require a much smaller amount of outside energy for the development of these resources. It may provide long-term, steady, and year-round employment of a highly technical nature. It may add to the income of the region where it is applied without adversely affecting the existing economy or way of life. It may operate in harmony with the natural landscape and with the physical characteristics of the resource and the area in which it is found, and may cause no harm to that area. In short, this invention offers an alternative method of extracting coalbed methane which may be superior to that currently employed.
Coalbed methane is a form of natural gas which is found at various sites in the western United States and elsewhere. It differs from conventional natural gas, which is confined to the interstices of porous rock formations which are overlain by an impermeable geologic stratum which keeps the gas from escaping into the atmosphere. Coalbed methane consists instead of various hydrocarbons which belong to the paraffin series of compounds, and which are dissolved in water which permeates certain coal beds found deep underground. It has been given the name coalbed methane because this gas is essentially the only one which can be readily extracted from the deposit by using the current method of drilling wells down into the coal beds from above.
This selective production results from the differing thermodynamic properties of the gaseous paraffins. Methane is only slightly soluble in water at atmospheric pressure, but its solubility increases rapidly as the pressure increases. Ethane is only marginally soluble in water at all pressures, and is therefore rare in saturated coal beds. Propane and butane are quite soluble in water at all pressures, including atmospheric. When a well is drilled into a water- and gas-saturated coal bed, the pressure of that water is almost instantaneously reduced to values near atmospheric. This drastically reduces the solubility of the methane in the water and causes it to bubble out rapidly, forming a lightweight froth which is forced upward through the well by the much higher pressure found in the coal bed surrounding the well. This pressure is so high that such wells are often artesian in nature, and tend to spew both gas and water into the air unless the well is quickly capped.
When this froth reaches the surface and is captured in a suitable container, it can easily be separated by gravity into methane and water. The methane is then pumped into pipelines for delivery to the market. But this superfluity of methane discharge lasts only a short time. The tiny portion of the coal bed punctured by each well quickly becomes exhausted of its limited supply of both water and methane, and the diffusion of both fluids through the coal from as yet untapped regions nearby proceeds very slowly. To keep the well producing, therefore, a pump must then be installed to force more methane-containing water to the surface. In order to speed up the supply, another process called hydraulic fracturing is often added. Water is pumped down the well into the coal bed at high pressures in order to break the coal into smaller fragments and thus expand the network of microscopic cracks through which diffusion normally takes place. Since the latter two named processesxe2x80x94pumping water upward and then pumping other water downwardxe2x80x94counteract each other, each process must be conducted for a limited time and then reversed for a comparable period. In between, long periods of inaction must be endured.
This method of extraction inevitably brings with it certain social, environmental, and economic side effects which at times can be quite severe. Since the wells must often penetrate thousands of feet of overburden before encountering the coal beds, very tall drilling rigs and very long sections of both drilling pipe and casing must be used in order to minimize the frequency of adding new sections. Thus the trucks transporting these materials to the drilling site must also be of great length. In order to accommodate this length, the roads leading to all sites must be made wide enough to allow these trucks to negotiate curves. Both these roads and the well sites themselves must be cleared of vegetation and flattened over extremely large expanses in order that the trucks and rigs can be maneuvered easily. This means that an open space covering dozens of acres must be cleared for each site surrounding a drill hole which may be only a foot or so in diameter. In places where the terrain is not flat, or where the soil is fragile, this disturbed land can be restored to its original condition only with great difficulty and at great expense.
In areas where coalbed methane wells have been drilled near homes supplied by water wells tapping into aquifers which lie above the coal beds, severe contamination of the water from these wells has occurred subsequent to the drilling of the methane wells. This contamination consists of hydrocarbons dissolved in the water, and has led to incidents such as water taps whose output can be ignited when opened, as well as gas-filled well houses which have exploded due to a spark of some kind. This situation, which definitely did not exist prior to the gas well drilling, was undoubtedly caused by propane, butane, and/or residual methane forced upward to the higher aquifers around the outside of the unsealed methane well casings.
The drilling of large and deep wells for methane, as well as other related processes, leads to loud persistent noise which often continues day and night. And the movement of energy company vehicles along the almost always unpaved roads serving the wells generates large and persistent dust clouds which cannot be confined to the well sites. Both of these aspects of the process cause severe annoyance to other residents of the vicinity. Moreover, the production of gas from each well is of limited duration, since the portion of the coal bed near it quickly becomes depressurized and dewatered. Thus the long-term exploitation of such a deposit requires repeated moving of the drilling and pumping equipment from one site to another. All of this disturbance is expected to continue for many years and to affect vast tracts of land, thus making it very difficult, if not impossible, for others to dwell in the same areas or to use the same land for other purposes without undergoing major unfavorable changes in their life styles.
Each well must be served by its own pipeline, and each of these must be connected to a network of larger pipelines leading to market areas. For safety purposes, all of these lines must be buried underground. In order to minimize the total length of the pipelines, they must be laid in lines as straight as possible, thus crossing numerous parcels of both public lands, which dominate the regions where coalbed methane is found, as well as many private parcels which have been owned and occupied by others for many years. Power of eminent domain has been granted to the energy companies to allow them to locate such lines where they wish, with other users having little voice in their location. The disruption due to this activity will also migrate from place to place as other portions of the coal beds are sequentially developed.
Many of the adverse effects of this process are site-specific. To cite one major example, one of the largest of all coalbed methane deposits lies in the Piceance Basin field located mainly in northwest Colorado and extending into adjacent portions of Wyoming and Utah. The water saturating the coal bed was derived primarily from humid mountains located on the periphery of this bowl and reaching as high as 14,000 feet in elevation, plus a number of large and high mesas capping the beds themselves. The center portion of the coal bed, which lies at lower underground elevations and is the richest in dissolved methane because of the higher water pressures found there, descends well below sea level. Thus the wells tapping the deposit here must be extremely deep, perhaps 15,000 feet or more in some places.
The geological conditions of the Piceance Basin field are quite unique. Except for the high peaks surrounding the bowl and some of the high mesas which cap the coal beds, the geologic formations under which the methane is found are notoriously unstable. Wherever the erosion-resistant capping mesas have been eroded away, the land surface is primarily made up of landslide deposits. This landslide process is still very active, as exemplified by the one-mile-square block which slid downhill only a few years ago, burying about a mile of Colorado State Highway 133 so deep that the new road had to be build on top of the slide. The landscape here and at other spots in the basin is thus very irregular in its topography, with very little level land being found anywhere. Because of these two factorsxe2x80x94irregular topography and low geologic stabilityxe2x80x94erosion due to future water runoff over land disturbed by the current coalbed methane process and inadequately restored is likely not only to be very severe, but also to persist for centuries. The practice of hydraulic fracturing of the coal beds adds to the likelihood that unwanted land movement will take place. It replaces coal deposits of moderate structural integrity with thick fluids consisting of coal fragments suspended in water. This material cannot support the overlying strata nearly as well as the undisturbed coal can. Therefore the probability of deep ground movement is greatly enhanced. This factor, combined with the low intrinsic geologic stability of the strata overlying the coal beds, can only result in increased rates of both landslide activity and subsequent surface erosion.
The land surrounding the methane field is primarily agricultural, with the local economy being highly dependent on the irrigation of orchards and other food crops, as well as hayfields and pasture land. Improperly checked erosion will inevitably cause wholesale disruption to this major part of the local economy and its accompanying life style through the lowering of stream beds and the siltation of both irrigation ditches and irrigated lands. Coalbed methane development will also adversely affect tourism, which forms another major portion of the present economy. Recreational activities, both for the local population and for visitors from all over the country, would also be sharply curtailed. A way of life which has existed here for well over a century could therefore be threatened by improper land restoration. This threat is further compounded by past and present experience regarding the State laws governing the restoration of land damaged by mineral extraction activities in the region. Enforcement of such laws has typically been either inadequate or nonexistent. As a result, considerable harm to established institutions by such temporary development has occurred frequently in the past.
Another factor specific to the Piceance Basin coalbed methane deposit may be of even greater concern, since it could adversely affect regions and populations up to a thousand miles away. In addition to methane, the water saturating such coal beds also contains large amounts of salt. In the Piceance Basin deposit, the salt content is extraordinarily high. Measurements taken from test wells in the area show salt contents ranging from 7 to 15%, or two to four times as high as that of sea water. And the Piceance Field is so vast that the total amount of salt it contains is greater than that found in Great Salt Lake. Since this salt inevitably comes out of the well with the water, suitable means must be provided for its subsequent disposal. One means which cannot be utilized, but unfortunately is being used at the present time, is simply to let gravity carry it away down the Colorado River. This river supplies all or part of the water supply, for both drinking and irrigation purposes, of a region populated by some 40 million people and extending from Colorado to Utah, Arizona, Nevada, southern California, and the Mexican states of Sonora and Baja Calif. It has been know for some time that the major contaminant in the river""s water is sodium. In the lower reaches of the river, the salt content is already so high at times that the water is unusable either for domestic or irrigation purposes. Additional sodium from inadequately controlled coalbed methane development could more than double this amount, thus causing a disaster which would dwarf the actions of the ancient Romans, who poured seawater on the fields of Carthage in order to permanently destroy the land""s usefulness.
Proponents of developing the Piceance Basin coalbed methane have proposed three methods of disposing of this water. One group suggested the construction of evaporating ponds held back by earthen dams located at various sites in the lower valleys of the region. They justified this proposition on the fact that the average annual evaporation rate at these semi-arid sites exceeds the average annual precipitation. But in some years, such as 1983, precipitation here was more than double the evaporation rate. If such a year should be repeatedxe2x80x94which is an eventual certaintyxe2x80x94all of these ponds would overflow and the salt would proceed downstream. The fertility of all lands irrigated with or flooded by this water could be destroyed as permanently as were those of Carthage. And perhaps even before this eventuality occurred, the dams would erode away due to inadequate maintenance and the same thing could happen more gradually. It doesn""t matter whether the land is subjected to such salinization a bit at a time or all at once; the effect would still be the same as it was in ancient Carthage.
The second plan is to re-inject the saline water down through another series of wells to some underground strata lying below the level of the coal beds and made up of porous rock which is now free of water. But the natural tendency of water to flow downhill, even below ground, makes it extremely unlikely that any strata possessing these particular characteristics really exist. Thus it is highly probable that this method would be even more futile than the first.
A third process also results in the extraction from the coalbeds of vast quantities of highly saline water which, if not disposed of properly, will inevitably and severely contaminate all downstream riverine water resources from the coalbed methane beds all the way to the sea. The proponents of this practice have offered promises of xe2x80x9ctreatmentxe2x80x9d of this water. Since this type of water pollution is a chemical phenomenon, any treatment of it may necessarily be of a chemical nature. The primary chemical pollutant found in this water is sodium, which can come from sodium chloride or other sodium salts. Unfortunately, this element cannot be removed from water by chemical means. The reason for this is that sodium has a greater chemical affinity for water than any other elements (with the possible exception of the similar but much rarer lithium). This is why sodium is used in water softeners. When added to hard water, it displaces the calcium and magnesium ions which are responsible for the hardness of water, causing these elements to be precipitated out of the solution in solid form. But this process cannot be used to remove sodium. This is why all desalinization plants must remove the water from the sodium instead of vice versa, employing distillation (evaporation) techniques. This is an extremely energy-consuming process, and it is doubtful that the coalbed methane water even contains sufficient methane to provide enough energy to accomplish this.
The quantity of this salt contamination from existing and proposed coalbed methane wells can be shown to be more than sufficient to completely destroy the usefulness of all of the domestic and irrigation water resources presently diverted from the Colorado, Missouri, and Rio Grande Rivers downstream from the coalbeds. These water resources now serve a population of more than 50 million people from Montana to Southern California and across all of northern Mexico. And even if we had enough energy from another source to provide this water purification, the problem of disposal of the salt which would remain behind would not be solved. There are only two known places where these billions of tons of salt could safely be disposed of. One of these is beyond the continental shelf of either the Atlantic or Pacific Ocean. Securely leakproof pipelines thousands of miles long would have to be built to accomplish this. The other safe site is a bit closer to the coalbed methane fields: the great salt flats of western Utah. This could conceivably be transported by rail, but this process as well might require more energy than is available within the coalbed methane fields.
Accordingly, an improved method and system for recovering coalbed methane have been developed. The method involves tunneling along a seam of coal to a point below a water table and at a depth below the water table sufficient for dissolved methane to be present in the water; separating a portion of the water containing dissolved methane while below the water table; reducing pressure on the separated portion for extracting dissolved methane; removing the extracted methane; and discharging the separated portion of water after extracting dissolved methane. The system for recovering coalbed methane comprises: a boring machine adapted for tunneling along a seam of coal to a point below a water table and to a depth below the water table sufficient for dissolved methane to be present in the water; a separator adapted for separating a portion of the water containing dissolved methane while below the water table and extracting dissolved methane from the separated portion; a first conduit adapted for removing the extracted methane; and a second conduit adapted for discharging the separated portion of water after the extraction of dissolved methane.